BRAINCAKEThe Power Stroke
In the resting state the myosin head has ADP and Pi bound. Once the binding site is exposed the myosin head releases Pi and binds to the actin molecule forming a cross-bridge. ADP is released and the head bends pulling the actin towards the middle of the sarcomere. The binding of ATP breaks the cross-bridge and the myosin head detaches. Hydrolysis of ATP returns the myosin head to its resting state. It is then free to bind to another binding site further along.
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Key terms in this lesson
- Sarcomere
- The contractile unit of a myofibril, delineated by two Z-lines, containing overlapping actin and myosin filaments.
- Actin
- A thin protein filament in a myofibril that, together with myosin, slides during muscle contraction.
- Myosin
- A thick protein filament in a myofibril with globular heads that bind to actin and pull it during muscle contraction.
- ATP
- Adenosine triphosphate, the universal energy currency of cells, which releases energy for cellular reactions when hydrolysed to ADP and inorganic phosphate.